The present invention relates to a polymerizable liquid crystal composition incorporating a polymerizable liquid crystal compound useful in applications such as optical phase retardation plates, polarizing plates, polarizing prisms, optical wave guides, piezoelectric elements, nonlinear optical elements, a variety of optical filters, liquid crystal pigments which utilize the selective reflection of cholesteric liquid crystal phases and the like, liquid crystalxe2x80x94resin composite displays, holographic liquid crystal displays, polymer stabilized liquid crystal (ferroelectric liquid crystal, antiferroelectric liquid crystal) displays, and as a coating for optical fibers or the like.
If a liquid crystal compound with a polymerizable functional group (hereafter referred to as a polymerizable liquid crystal compound), or a polymerizable liquid crystal composition incorporating this type of compound is aligned in the liquid crystal state, and subsequently irradiated with an activated energy beam such as ultraviolet light or the like, then a polymer can be prepared in which the aligned state of the liquid crystal molecule is fixed. Because polymers prepared in this manner display anisotropy of physical properties such as the refractive index, dielectric constant, magnetizability, modulus of elasticity and thermal expansion coefficient, they can be readily applied as optical phase retardation plates, polarizing plates, polarizing prisms, optical wave guides, piezoelectric elements, nonlinear optical elements, a variety of optical filters, liquid crystal pigments which utilize the selective reflection of cholesteric liquid crystal phases and the like, and as a coating for optical fibers or the like.
An example of a polymerizable liquid crystal composition used for such applications is provided in Japanese Unexamined Patent Application, First Publication No. Hei-8-3111, in which a polymerizable liquid crystal composition incorporating a liquid crystal compound with one (meth)acrylic group in each molecule is disclosed. The polymerizable liquid crystal composition disclosed in this application has the distinction of displaying liquid crystallinity at room temperature, although problems exist in that both the transparency following polymerization and the mechanical strength of the polymerized product are inferior.
Published Japanese Translation No. Hei-6-507987 of PCT International Publication (U.S. Pat. No. 5,871,665), Japanese Unexamined Patent Application, First Publication No. Hei-10-310612 (EP-A 869112), Published Japanese Translation No. Hei-11-513360 of PCT International Publication (U.S. Pat. No. 5,833,880), DE-A 4226994, GB-A 2306470, and Int. Pat. Application 98-23580 disclose liquid crystal compounds with two polymerizable functional groups such as a (meth)acrylic group within a single molecule, and polymerizable liquid crystal compositions incorporating such liquid crystal compounds. The compounds disclosed in these publications have a partial structural feature wherein at least one of the two polymerizable functional groups is connected to a ring A through a linking chain such as an alkyleneoxy group, and this ring A is then connected to a separate ring B, either directly, or through an ether coupling, a thioether coupling, an alkylene group, an oxyalkylene group, an alkyleneoxy group, a carbonyl group, an ester coupling, a thioester coupling, a vinyl group, a vinyl carbonyl oxy group, a vinyl alkylene group, an alkylene vinyl group, a methylimino group, an azo group or an amide group.
Of these compounds, those compounds with no ring substitution groups have a lower limit temperature for the nematic phase of at least 100xc2x0 C., whereas a portion of those compounds with a substituted group on the ring such as a fluorine atom, a methyl group, a methoxy group or a methyl carbonyl group, display a lower limit of the nematic phase temperature which has been reduced to approximately 60xc2x0 C. The polymerizable liquid crystal composition is aligned uniformly while in the liquid crystal state, and with this liquid crystal state maintained, is subsequently irradiated with an energy beam such as an ultraviolet light beam to effect a photopolymerization and semi-permanently fix the uniformly aligned state. Consequently, if the lower limit temperature for the nematic phase is higher than room temperature, then heating is required to maintain the liquid crystal state and ensure the uniform alignment, and as a result of this heating, unintended thermal polymerization will also be induced, in addition to the photopolymerization resulting from the energy beam irradiation, and such thermal polymerization can cause an undesirable loss of the uniformly aligned state of the liquid crystal molecules, meaning a non-uniform alignment state different from the desired state of uniform alignment will be fixed. In addition, a further problem arises in that in order to use these materials to prepare a polymerizable liquid crystal composition which displays a nematic phase within a highly workable temperature range from room temperature to approximately 40xc2x0 C., where thermal polymerization is not induced, a combination of a large variety of liquid crystal compounds must be used. Furthermore, compounds with substituted groups on the ring are complicated to synthesize, and also display inferior adhesion to substrates, particularly in the case of compounds with a fluorine atom on the ring.
Furthermore, the compounds described in Japanese Unexamined Patent Application, First Publication No. Hei-10-310612 (EP-A 869112) and Int. Pat. Application 98-23580 comprise a plurality of cross-linkable intermediate phase (liquid crystal phase) forming residues within each molecule, and consequently suffer from a tendency to solidify into a glass like form. Moreover, because the molecular weight is large at 1000 to 3000, the viscosity is also high, and so these compounds also suffer from a lack of compatibility with other polymerizable liquid crystal compounds.
In addition, Japanese Unexamined Patent Application, First Publication No. Hei-9-40585 (U.S. Pat. No. 5,800,733) and Japanese Unexamined Patent Application, First Publication No. Hei-9-52857 (EP-A 755915) disclose compounds comprising a structure in which two cross-linkable intermediate phase (liquid crystal phase) forming residues are bonded to positions 1 and 2 of a six membered ring. These compounds do not display a nematic phase, and a portion of the compounds disclosed display a smectic A phase, although this smectic A phase suffers from a high viscosity and poor alignment.
Moreover, xe2x80x9cLiquid Crystalsxe2x80x9d, (Vol. 24, No. 3, pp. 375-379, 1998) discloses an impurity generated during synthesis of 2-(alkenyloxyphenyloxy)-5-(hydrothioalkyleneoxy phenyloxy) toluene, with a structure in which the hydrothio group of the compound and 4-hydrothioalkyleneoxy benzoic acid are bonded together. However in this document, disclosure is limited to the specifying of this compound as an impurity, and absolutely no comment is made regarding the use of this compound specified as an impurity for application to polymerizable liquid crystal compositions.
An object of the present invention is to provide a polymerizable liquid crystal composition incorporating a polymerizable liquid crystal compound which even without the introduction of ring substitution groups such as fluorine atoms, displays a low nematic phase temperature, displays excellent compatibility with other polymerizable liquid crystal compounds, and furthermore yields a product following polymerization of good transparency and mechanical strength.
On the basis of extensive research on the correlation between the chemical structure of liquid crystal compounds with polymerizable properties and the physical properties of such compounds, the inventors discovered that by using a liquid crystal compound comprising a ring (A) to which a polymerizable functional group is bonded and a ring (H) which is connected to the ring (A) through either a carbonyloxyalkyleneoxy group or an oxyalkylenecarbonyloxy group (D), the problems outlined above could be resolved, and were consequently able to complete this invention.
In other words, in order to resolve the aforementioned problems, the present invention provides (A) a polymerizable composition which displays a liquid crystal phase, and moreover incorporates a liquid crystalline backbone with two or more rings, and a compound (I) with a partial structure represented by the general formula
P1xe2x80x94S1xe2x80x94A1xe2x80x94D1xe2x80x94E1xe2x80x94
[wherein P1 represents a polymerizable functional group;
S1 represents a linkage chain selected from the group consisting of xe2x80x94(CH2)wxe2x80x94, xe2x80x94O(CH2)wxe2x80x94, xe2x80x94(CH2)wOxe2x80x94, xe2x80x94(CH2)wC(xe2x95x90O)Oxe2x80x94, xe2x80x94(CH2)wOC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)O(CH2)wxe2x80x94 and xe2x80x94OC(xe2x95x90O)(CH2)wxe2x80x94 (wherein w represents an integer from 1 to 20);
A1 and E1 each represent, independently, a hydrocarbon ring or a hetero ring, although E1 is a ring incorporated within the liquid crystal backbone.
and D1 represents a linkage chain represented by xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)mxe2x80x94Oxe2x80x94, xe2x80x94O(CH2)mxe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94(CH2)mxe2x80x94Oxe2x80x94, or xe2x80x94O(CH2)mxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94 (wherein m represents an integer from 1 to 15)].
Furthermore, in order to resolve the aforementioned problems, the present invention also provides (B) an optically anisotropic film comprising a polymer obtained by polymerizing a polymerizable liquid crystal composition according to (A) above.
In addition, in order to resolve the aforementioned problems, the present invention also provides (C) an optical low pass filter comprising an optically anisotropic film according to (B) above as a structural element.